1. Technical Field
The invention relates to air brake systems for motor vehicles and more particularly to a air brake system condition monitoring system providing prognostic and diagnostic functionality.
2. Description of the Problem
Motor vehicle air brake systems rely on air compressors to supply pressurized air to air tanks which in turn supply air, under pressure, to the brake system. The tanks also typically supply air for brakes on trailers pulled by the tractor and may be used to supply air to other vehicle and trailer systems such as air suspension systems. Fault free operation of the air compressor, storage and distribution system are required for reliable and predictable brake operation.
Air brake systems can develop leaks upstream from, at and downstream from the tanks. The system air compressor can deteriorate over time, causing increases in tank charging times. Water can infiltrate storage tanks. All of these factors can affect reliability and effectiveness of the brake system.
To avoid unexpected failure of the air brake system, periodic verification that the compressor, pressurized air storage tanks and air brake lines are in good order is essential. However, manual inspection of these items is time consuming. It has been estimated that 80% of mechanics' time is spent on problem diagnosis. Much potential exists for time saving by use of on board diagnostic systems which can narrow the scope of potential problems to investigate and can provide a prognosis of developing problems.
Manual and visual inspections of air brake systems are done during daily pre-trip inspections. If tank leakage rates or tank charge times are higher that Department of Transportation established maximums, repair is required. Since pre-trip inspections may be unevenly performed, and since precision in measurement suffers due to low resolution of visual gauges, the reliability of such inspections is questionable. In addition, the ability to provide prognoses for developing problems where the multiple indicia must be correlated, is highly problematical. This can force maintenance to be based on mileage rather than need.
Pressure in an air brake system is typically measured only for the compressed air storage tanks. The air compressor on a truck is under the control of a governor which controls compressor operation in response to measured tank pressure. The point where the governor engages compressor operation is called the cut-in pressure. The governor responds to pressure in the system reaching an upper limit to cause the air compressor to discontinue supplying pressurized air. This point termed the cut-out pressure. A monitoring, prognostic and diagnostic system which requires pressure data only from a tank pressure sensor would be advantageous.